Absorption Cross-section Data Research Articles

Measurement of Photoneutrons from Depleted Uranium and Comparison Study Using MCNPX-PoliMi

High-energy photon interrogation is a nondestructive technique that is used to detect special nuclear materials and characterize nuclear waste. The development of such systems is complex and requires Monte Carlo simulations to optimize system performance. Monte Carlo simulations rely on various scattering, absorption, and photonuclear cross-section data. While the scattering and absorption cross-section data have been extensively studied and validated with experiments, the results obtained from photonuclear simulations are often found to underpredict measured results, indicating uncertainties in the photonuclear cross sections themselves. Thus, there is a need for new measured results that can be used to quantify underpredictions in simulations using photonuclear cross-section data. In the present work, we interrogated depleted uranium with a 9-MV electron linac and detected photoneutrons with trans-stilbene organic scintillators. The measurement of photoneutrons with organic scintillators is challenging due to the presence of the intense photon flux, which causes issues such as pulse pile-up, detector saturation, and poor signal-to-background ratio. To mitigate these challenges, we used iron and polyethylene shielding of varying thicknesses around the depleted uranium target and a neural network–based digital pulse processing algorithm to recover neutron and photon information from piled-up events. Our goal was to compare the measured photoneutron count rate with the simulated rate obtained using the MCNPX-PoliMi transport code. For a light output window of 0.28 to 2.67 MeVee (1.66- to 6.85-MeV proton recoil energy), we found that the simulated count rate obtained using the ENDF/B-VII photonuclear cross-section library underpredicts the measured rate by 32.8% ± 3.2%. Additionally, we compared the simulated and measured photoneutron light output distributions. For the least thicknesses of shielding, the simulation was found to underpredict measurements in the 0.70- to 2.67-MeVee light output window. For the greatest thicknesses of shielding, the simulation was found to underpredict the measurement across the entire light output window of 0.28 to 2.67 MeVee.

High band-width mid-infrared frequency-modulated Faraday rotation spectrometer for time resolved measurement of the OH radical.

We present a novel mid-infrared frequency-modulated Faraday rotation spectrometer (FM-FRS) for highly sensitive and high bandwidth detection of OH radicals in a photolysis reactor. High frequency modulation (up to 150 MHz) of the probe laser using an electro-optical modulator (EOM) was used to produce a modulation sideband on the laser output. An axial magnetic field was applied to the multi-pass Herriott cell, causing the linearly polarized light to undergo Faraday rotation. OH radicals were generated in the cell by photolyzing a mixture of ozone (O3) and water (H2O) with a UV laser pulse. The detection limit of OH reaches 6.8 × 108 molecule/cm3 (1σ, 0.2 ms) after 3 and falling to 8.0 × 107 molecule/cm3 after 100 event integrations. Relying on HITRAN absorption cross section and line shape data, this corresponds to minimum detectable fractional absorption (Amin) of 1.9 × 10-5 and 2.2 × 10-6, respectively. A higher signal-to-noise ratio and better long-term stability was achieved than with conventional FMS because the approach was immune to interference from diamagnetic species and residual amplitude modulation noise. To our knowledge, this work reports the first detection of OH in a photolysis reactor by FM-FRS in the mid-infrared region, a technique that will provide a new and alternative spectroscopic approach for the kinetic study of OH and other intermediate radicals.

Sensitivity Analysis of 1,3-Butadiene Monitoring Based on Space-Based Detection in the Infrared Band

The monitoring of the Volatile Organic Compounds (VOCs) in the atmosphere is of great significance for reducing chemical pollution, warning of fires, and improving air quality. Among the VOCs, 1,3-butadiene is essential to monitor as a carcinogenic environmental pollutant. The space-based detection of 1,3-butadiene was made possible by recently development of infrared detection satellites and advances in spectroscopic techniques. In this work, based on the demand for space-based infrared detection of 1,3-butadiene, a modeling method of Earth background radiance characteristics coupled with remote sensing data and physical model is proposed, which can effectively simulate the Earth background radiance field distribution under any atmospheric conditions. Specifically, infrared spectral radiance of 1,3-butadiene was simulated from absorption cross-section data. Further, combined with the radiative transfer model and atmospheric profiles of satellite sensor data, such as temperature, pressure, and H2O and O3 mixing ratio, the atmospheric transmittance and atmospheric background radiance are simulated. Finally, infrared space-based detection of 1,3-butadiene is simulated by coupling Earth background radiance and the detectability is analyzed and discussed by using signal-to-clutter ratio (SCR). The results show that 1,3-butadiene has an absorption effect in space-based infrared detection. The detectability of the narrow band 9.8–10.0 μm and 10.9–11.1 μm is better than that of the wide band 9.0–12.0 μm, and 10.9–11.1 μm is a better detection band for 1,3-butadiene than other bands. This paper provides a method for the space-based infrared detection of 1,3-butadiene. It also provides a reference for selecting the appropriate band for the detector.

MID-IR laser absorption spectroscopy of 1- and 2-butanol in a shock tube facility

E-fuels are CO2-neutral fuels generated using renewable fuels such as wind and solar energy, where the carbon is taken out of the atmosphere or from biomass. One of the suitable e-fuel classes are alcohols with a low number of carbon atoms. Obtaining the low pollutant emissions on combusting liquid fuels such as fuel oil and kerosene, e-fuels with lean, premixed, pre-vaporized (LPP) concept plays a pivotal role. So, in this framework, the present work focuses on the combustion properties in the low pressure and high-temperature regime of 1- and 2-butanol isomers to evaluate their potential as future sustainable aviation fuels. The study investigates the fuel-lean conditions of 1- and 2-butanol in the fuel/oxygen equivalence ratios of 0.25, 0.5, and 0.9 relevant to the LPP (Yan et al. 2015) combustion concept for its applications in aviation. The flame chemistry of butanol isomers has been widely investigated; however, more investigations on ignition chemistry are needed. For this, tunable diode laser absorption spectroscopy is utilized to obtain the time-resolved CO formation history, ignition delay time (IDT), and progress in the butanol consumption by applying the central wavelength of 2059.91 cm−1 and 2948.27 cm−1, respectively. The measurements were performed in the temperature range of 1150–1500 K near 1.5 and 3 bar. The experimentally obtained IDT were validated with several recent reaction mechanisms available in the literature. The correlation between measured IDT, CO formation, and butanol consumption data was captured by the simulations satisfactorily. However, the CO formation from the simulation shows disagreement with the experimentally obtained signal. In addition, discrepancies in the absolute CO were observed between simulation and experiment. Moreover, a sharp drop was observed for the butanol consumption histories predominantly at ϕ= 0.9 in both 1-and 2-butanol, which could not be predicted from the available mechanisms. Furthermore, by updating the rate constants of several key reactions near the sharp fall region, a better prediction from the mechanism was seen. The time-resolved CO profile and butanol consumption history, along with the absorption cross-section data for 1- and 2-butanol isomers, are reported for the first time in this paper.

The ω-absorption line distribution function for rank correlated SLW model prediction of radiative transfer in non-uniform gases

Unlike previous global methods, the recently developed Rank Correlated Spectral Line Weighted-sum-of-gray-gases (RC-SLW) model does not require specification of a reference gas thermodynamic state from which all other states are corrected using a correlated spectrum assumption. However, the RC-SLW approach still requires specification of an arbitrary blackbody source temperature to generate the Absorption Line Blackbody Distribution Function (ALBDF) used in construction of the spectral model. This paper reports on the development of a universal RC-SLW model that eliminates the need for the specification of a blackbody source temperature. The approach replaces the ALBDF with a new spectral distribution function, herein termed the ω-Absorption Line Distribution Function (ω-ALDF), and is based on a new spectral weighting function instead of the Planck blackbody distribution function. The ω-ALDF presented here depends only on the local gas thermodynamic state, and does not involve the blackbody source temperature used in the ALBDF. The new weighting function is determined using the well-established ALBDF, avoiding the need to generate a radically new distribution function database from the detailed gas absorption cross-section data. The ω-ALDF based RC-SLW model thus requires no user-specified parameters (no reference thermodynamic state and no blackbody source temperature). Further, only minor modification of the conventional RC-SLW model is needed to implement the new approach. Development of this new distribution function is only possible within the theoretical framework of the Rank Correlated SLW model. This work presents the theoretical development of the ω-ALDF, and demonstrates the use and accuracy of this new universal RC-SLW model.

Comparison of the RADM2 and RACM chemical mechanisms in O3 simulations: effect of the photolysis rate constant

Since the photolysis rate plays an important role in any photoreaction leading to compound sink and radical formation/destruction and eventually O3 formation, its impact on the simulated O3 concentration was evaluated in the present study. Both RADM2 and RACM were adopted with and without updated photolysis rate constants. The newly developed photolysis rates were determined based on two major absorption cross-section and quantum yield data sources. CMAQ in conjunction with meteorological MM5 and emission data retrieved from Taiwan and East Asia were employed to provide spatial and temporal O3 predictions over a one-week period in a three-level nested domain [from 81 km × 81 km in Domain 1 (East Asia) to 9 km × 9 km in Domain 3 (Taiwan)]. Four cases were analyzed, namely, RADM2, with the original photolysis rates applied in Case 1 as a reference case, RADM2, with the updated photolysis rates applied in Case 2, and RACM, with and without the updated photolysis rates applied in Cases 3 and 4, respectively. A comparison of the simulation and observed results indicates that both the application of updated photolysis rate constants and RACM instead of RADM2 enhanced all three error analysis indicators (unpaired peak prediction accuracy, mean normalized bias error and mean absolute normalized gross error). Specifically, RADM2 with the updated photolysis rates resulted in an increase of 12 ppb (10%) in the daily maximum O3 concentration in southwestern Taiwan, while RACM without the updated photolysis rates resulted in an increase of 20 ppb (17%) in the daily maximum O3 concentration in the same area. When RACM with the updated photolysis rate constants was applied in the air quality model, the difference in the daily maximum O3 concentration reached up to 30 ppb (25%). The implication of Case 4 (RACM with the updated photolysis rates) for the formation and degradation of α-pinene and d-limonene was examined.

Impact of using a new ultraviolet ozone absorption cross-section dataset on OMI ozone profile retrievals

Abstract. We evaluate different sets of high-resolution ozone absorption cross-section data for use in atmospheric ozone profile measurements in the Hartley and Huggins bands with a particular focus on BDM 1995 (Daumont et al. 1992; Brion et al., 1993; Malicet et al., 1995), currently used in our retrievals, and a new laboratory dataset by Birk and Wagner (2018) (BW). The BDM cross-section data have been recommended to use for retrieval of ozone profiles using spaceborne nadir-viewing backscattered ultraviolet (BUV) measurements since its improved performance was demonstrated against other cross-sections including Bass and Paur (1985) (BP) and those of Serdyuchenko et al. (2014) and Gorshelev et al. (2014) (SER) by the “Absorption Cross-Sections of Ozone” (ACSO) activity. The BW laboratory data were recently measured within the framework of the European Space Agency (ESA) project SEOM-IAS (Scientific Exploitation of Operational Missions – Improved Atmospheric Spectroscopy Databases) to provide an advanced absorption cross-section database. The BW cross-sections are made from measurements at more temperatures and in a wider temperature range than BDM, especially for low temperatures. Relative differences of cross-sections between BW and BDM range from ∼2 % at shorter UV wavelengths to ∼5 % at longer UV wavelengths at warm temperatures. Furthermore, these differences dynamically increase by up to ±40 % at cold temperatures due to no BDM measurements having been made below 218 K. We evaluate the impact of using different cross-sections on ozone profile retrievals from Ozone Monitoring Instrument (OMI) measurements. Correspondingly, this impact leads to significant differences in individual ozone retrievals by up to 50 % in the tropopause where the coldest atmospheric temperatures are observed. Bottom atmospheric layers illustrate the significant change of the retrieved ozone values, with differences of 20 % in low latitudes, which is not the case in high latitudes because the ozone retrievals are mainly controlled by a priori ozone information in high latitudes due to less photon penetration down to the lower troposphere. Validation with ozonesonde observations demonstrates that BW and BDM retrievals show altitude-dependent bias oscillations of similar magnitude relative to ozonesonde measurements, much smaller than those of both BP and SER retrievals. However, compared to BDM, BW retrievals show significant reduction in standard deviation, by up to 15 %, especially at the coldest atmospheric temperatures. Such improvement is achieved mainly by the better characterization of the temperature dependence of ozone absorption.

Shock tube measurement of NO time-histories in nitromethane pyrolysis using a quantum cascade laser at 5.26 µm

The pyrolysis of nitromethane, CH3NO2, was studied at ∼3.5 atm and 1013 K–1418 K in a heated shock tube by measuring the key product nitric oxide (NO) using mid-infrared laser absorption spectroscopy. We used a quantum cascade laser (QCL) at 5.26 µm to exploit the strong NO absorption at 1900.08 cm−1. With the NO absorption cross-section data characterized at 1006 K–1789 K and 2.7 atm–3.5 atm behind reflected shock waves, we measured the NO concentration time-histories during the pyrolysis of nitromethane at two different concentrations (1.05% and 0.6%). The absorption interference from other major products such as CO and H2O was analyzed to be negligible, leading to an interference-free NO diagnostic in nitromethane pyrolysis. A recent kinetic model of Shang et al. (2019) was adopted to interpret the shock tube data. All the NO time-histories measured over the entire temperature range 1013 K–1418 K were well-predicted by this model in terms of the initial NO formation rate and the final plateau level. The rate-of-production, sensitivity, and reaction flux analyses were performed to identify four important reactions (CH3NO2 = CH3 + NO2, CH3NO2 ↔ CH3ONO = CH3O + NO, CH3 + NO2 = CH3O + NO, and NO2 + H = NO + OH) that determine the NO formation during CH3NO2 pyrolysis. The satisfactory agreement between the simulation and shock tube/laser absorption measurement further validated the kinetic mechanism of nitromethane decomposition. The developed mid-infrared NO absorption sensor provides a promising diagnostic tool for studying fuel-nitrogen chemical kinetics in the shock tube experiments.

The Reaction NCN + H2: Quantum Chemical Calculations, Role of 1NCN Chemistry, and 3NCN Absorption Cross Section.

The NCN radical plays a key role for modeling prompt-NO formation in hydrocarbon flames. Recently, in a combined shock tube and flame modeling study, the so far neglected reaction NCN + H2 and the related chemistry of the main product HNCN turned out to be significant for NO modeling under fuel-rich conditions. In this study, the reaction has been thoroughly revisited by detailed quantum chemical rate constant calculations both for the singlet 1NCN and triplet 3NCN pathways. Optimized geometries and vibrational frequencies of reactants, products, and transition states were calculated on B3LYP/aug-cc-pVQZ level with single-point energy calculations carried out against the optimized structures using CASPT2/aug-cc-pVQZ. The determined rate constants for the 1NCN + H2 reaction as well as the newly measured high temperature absorption cross section of 3NCN made a reevaluation of the shock tube data of the previous work necessary, finally revealing quantitative agreement between experiment and theory. Moreover, the new directly measured Doppler-limited absorption cross section data, σ(3NCN, λ = 329.1302 nm) = 2.63 × 109 × exp(-1.96 × 10-3 × T/K) cm2/mol (±23%, p = 0 bar, T = 870-1700 K), are in agreement with previously reported values based on detailed spectroscopic simulations. Hence, a long-standing debate about a reliable high temperature 3NCN absorption cross section has been resolved. Whereas 3NCN + H2 resembles a simple abstraction type reaction with the exclusive products HNCN + H, the singlet radical reaction is initiated by the insertion into the H-H bond. Up to pressures of 100 bar, the main products of the subsequent decomposition of the H2NCN intermediate are HNCN + H as well, with minor contributions of CN + NH2 toward higher temperatures. Although much faster than the triplet reaction, the singlet radical insertion is actually rather slow, due to the necessary reorganization of the HOMO electron density in 1NCN that is equally distributed over the two N atom sites. In general, the distinct reactivity differences call for a separate treatment of 1NCN and 3NCN chemistry. However, as the main reaction products in case of the H2 reaction are the same and as the population of the 1NCN in thermal equilibrium remains low, a properly weighted effective rate constant k(NCN + H2 → HNCN + H) = 2.62 × 104 × (T/K)2.78 × exp(-97.6 kJ/mol/RT) cm3 mol-1s-1(±30%, 800 K < T < 3000 K, p < 100 bar) is recommended for inclusion into flame models that, as yet, do not explicitly account for 1NCN chemistry.

Application of temperature dependent ozone absorption cross-sections in total ozone retrieval at Kunming and Hohenpeissenberg stations

We analyzed the temperature dependence of ozone absorption cross-sections in four data sets: the quadratic temperature data based on measurements of Bass and Paur (BPQ); data measured with the SCIAMACHY satellite spectrometer (SAC); data derived by Daumont, Brion, and Malicet (DBM); and data determined by Serdyuchenko et al. from the University of Bremen (SER). The ozone effective absorption coefficients of the Dobson and Brewer instruments at Kunming in the low-latitude stations and Hohenpeissenberg in the middle-latitude stations were calculated. The test of the total ozone column (TOC) from different ozone absorption cross-section data sets shows that in the Dobson and Brewer retrieval algorithms, the effect of temperature on the Brewer instrument is smaller than that for the Dobson instrument. The temperature sensitivity of the two instruments to the SAC is −0.005%°C−1 and 0.102%°C−1, respectively, indicating that the differences in the temperature sensitivity result in differences in the TOC measurements between the two instruments, as well as in systematic seasonal differences. Using BPQ, DBM and SER to retrieve TOC will increase the overall deviation of the two instruments by 2.5%, −2.77% and −1.89%, respectively. The consistency of the TOC retrieval in the two instruments is the best when using the SAC, which shows a deviation of only 0.03%. The systematic seasonal deviation can also be effectively improved. In addition, this work makes up for the lack of relevant research in low-latitude areas. The rangeability of the monthly mean value of the instrument system deviation at a low-latitude station is about one-half of that at the mid-latitude station (Kunming: 0.2%–1.1%, Hohenpeissenberg: 0.2%–2.0%). This is because the vertical distribution of the ozone and temperature varies in different latitudes, the seasonal variation in the middle and high latitudes is significant, and the effective temperature of ozone (Teff) in low latitudes changes little.

A new photometric ozone reference in the Huggins bands: the absolute ozone absorption cross section at the 325 nm HeCd laser wavelength

Abstract. The room temperature (294.09 K) absorption cross section of ozone at the 325 nm HeCd wavelength has been determined under careful consideration of possible biases. At the vacuum wavelength of 325.126 nm, thus in a region used by a variety of ozone remote sensing techniques, an absorption cross-section value of σ = 16.470×10−21 cm2 was measured. The measurement provides the currently most accurate direct photometric absorption value of ozone in the UV with an expanded (coverage factor k = 2) standard uncertainty u(σ) = 31×10−24 cm2, corresponding to a relative level of 2 ‰. The measurements are most compatible with a relative temperature coefficient cT = σ−1 ∂ Tσ = 0.0031 K−1 at 294 K. The cross section and its uncertainty value were obtained using generalised linear regression with correlated uncertainties. It will serve as a reference for ozone absorption spectra required for the long-term remote sensing of atmospheric ozone in the Huggins bands. The comparison with commonly used absorption cross-section data sets for remote sensing reveals a possible bias of about 2 %. This could partly explain a 4 % discrepancy between UV and IR remote sensing data and indicates that further studies will be required to reach the accuracy goal of 1 % in atmospheric reference spectra.

Determination of europium content in Li2SiO3(Eu) by neutron activation analysis using Am-Be neutron source

Circulardiscs of Li2SiO3 doped with europium were prepared and a new activation procedure for the neutron dose estimation in a breeder blanket of fusion reactor is described. The amount of europium in the disc was determined by neutron activation analysis (NAA) using an isotopic neutron source. The average neutron absorption cross section for the reaction was calculated using neutron distribution of the Am-Be source and available neutron absorption cross section data for the 151Eu(n,γ)152mEu reaction, which was used for estimation of europium in the pallet. The cross section of the elements varies with neutron energy, and the flux of the neutrons in each energy range seen by the nuclei under investigation also varies. Neutron distribution spectrum of the Am-Be source was worked out prior to NAA and the effective fractional flux for the nuclear reaction considered for the flux estimation was also determined.

Absorption of Near UV Light by HNO3/NO3(-) on Sapphire Surfaces.

We have determined absorption of the near UV light (290-345 nm) by nitric acid (HNO3) deposition on sapphire window surfaces as a function of the HNO3 pressure, by using Brewster angle cavity ring-down spectroscopy. Apparent monolayer HNO3 surface absorption cross sections have been obtained; they range between (1.7 ± 1.1) × 10(-19) and (0.29 ± 0.03) × 10(-19) cm(2)/molecule. When nitric acid cross section values on sapphire surfaces were divided by those on fused silica surfaces for which only molecular HNO3 adsorption was reported, a new absorption band appeared in the 320-345 nm region. The shape of this absorption band is similar to that reported for surface nitrate (NO3(-)) at quartz/water interfaces, but is red-shifted by about 10 nm. Our study suggests that a small percentage (<7%) of adsorbed HNO3 formed by HNO3 deposition on sapphire surfaces is dissociated into surface nitrate on the time scale of about 5-7 min. Background transmission changes in the 320-350 nm region after exposing clean sapphire surfaces with many repeated HNO3 deposition/evacuation cycles are consistent with surface nitrate formation. We obtained nitrate surface absorption cross section data over 320-350 nm range. We also modeled photolysis rates of HNO3/NO3(-) on urban grimes. Atmospheric implications of the results are discussed.

Yb:Lu2O3 hydrothermally-grown single-crystal and ceramic absorption spectra obtained between 298 and 80 K

The hydrothermal growth, doping, and low temperature spectral characterization of Yb doped Lu2O3 was investigated. The absorption of the lutetia-based sesquioxide laser material Yb:Lu2O3 at temperatures of 80, 150, 200, 250, and 298K, in the wavelength range of 850–1100nm are reported. Data for both single crystal and ceramic Yb:Lu2O3 were obtained. The resulting absorption cross-section data will enable the further evaluation of Yb:Lu2O3 as a very promising high power cryogenic laser material.

Spectral properties of hydrothermally-grown Nd:LuAG, Yb:LuAG, and Yb:Lu2O3 laser materials

We have investigated the hydrothermal growth of, and spectrally characterized, the lutetium based laser materials Nd:LuAG, Yb:LuAG, and Yb:Lu2O3. Absorption cross-section data are presented for Nd:LuAG at 83, 175, and 295K. Absorption cross-section data was also obtained for Yb:LuAG at 83, 175, and 295K; the 295K data was used to generate emission cross-sections using the method of reciprocity. For Yb:Lu2O3, we present absorption cross-sections at 295K as well as emission cross-sections derived using reciprocity.

Sensitivity of stratospheric ozone lidar measurements to a change in ozone absorption cross-sections

The effect of a change in ozone absorption cross-section data is evaluated for stratospheric ozone lidar measurements, which are regularly performed for the monitoring of the ozone layer. The change is analysed for the measurements based on both the elastic and Raman scattering of the laser light by the atmosphere. The latter technique is essentially used for measurements performed in the presence of volcanic aerosol layers in the stratosphere. The discrepancy in ozone number densities is evaluated for various ozone cross-section data sets, using an atmospheric model for the evaluation of ozone cross-section temperature dependence. Results show that the difference in both elastic and Raman DIAL retrievals is below 1.5% in absolute values from 10 to 30km. Above 30km, the difference, estimated for the elastic DIAL retrieval only, is maximum around 45km, with largest differences reaching 1.8% in the tropics.

The Atmospheric Photolysis ofo-Tolualdehyde

The photolysis of o-tolualdehyde by natural sunlight has been investigated at the large outdoor European Photoreactor (EUPHORE) in Valencia, Spain. The photolysis rate coefficient was measured directly under different solar flux levels, with values in the range j(o-tolualdehyde) = (1.62-2.15) × 10(-4) s(-1) observed, yielding an average value of j(o-tolualdehyde)/j(NO(2)) = (2.53 ± 0.25) × 10(-2). The estimated photolysis lifetime is 1-2 h, confirming that direct photolysis by sunlight is the major atmospheric degradation pathway for o-tolualdehyde. Published UV absorption cross-section data were used to derive an effective quantum yield (290-400 nm) close to unity, within experimental error. Possible reaction pathways for the formation of the major photolysis products, benzocyclobutenol (tentatively identified) and o-phthalaldehyde, are proposed. Appreciable yields (5-13%) of secondary organic aerosol (SOA) were observed at EUPHORE and also during supplementary experiments performed in an indoor chamber using an artificial light source. Off-line analysis by gas chromatography-mass spectrometry allowed identification of o-phthalaldehyde, phthalide, phthalic anhydride, o-toluic acid, and phthalaldehydic acid in the particle phase.

Emission and Absorption Cross-Sections of Mg/Er-Codoped Near-Stoichiometric ${\rm LiNbO}_{3}$ Crystals

Near-stoichiometric (NS) (Mg:) Er:LiNbO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> crystals were grown from melts ([Li <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> O]:[Nb <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> O <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">5</sub> ] = 1:1) containing 0.0/0.5, 0.5/0.5, and 1.0/0.5 mol%/mol% MgO/Er <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> O <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> . OH absorption study shows that the optical damage threshold Mg concentration of the Er/Mg-codoped NS crystal is just near 1.0 mol%. Polarized visible and near infrared, and unpolarized mid-infrared (2.7 μm, <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">4</sup> I <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">11/2</sub> → <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">4</sup> I <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">13/2</sub> ) emission spectra of Er <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3+</sup> ion in these crystals were measured. From measured emission spectra, the emission and absorption cross-section spectra were calculated based upon McCumber theory, and compared with the data of congruent Er:LiNbO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> bulk material and/or Ti-diffused Er:LiNbO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> strip waveguide and the results obtained from the direct unpolarized optical absorption measurements. The 550, 980, and 1530 nm emission lifetimes were also measured, and compared with the Judd-Ofelt theoretical values and the measured values of the congruent material. The results show that the polarized absorption cross-section data derived from the emission spectra are comparable to the unpolarized cross-section data from direct absorption measurements. The emission and absorption cross-sections, their polarization dependences as well as the lifetime all change definitely as the crystal composition shifts from the congruent point to the near-stoichiometry. In the NS crystal, the Er <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3+</sup> ion has smaller emission and absorption cross-sections, and longer lifetimes. In contrast, MgO codoping has less effect on the emission and absorption cross-sections, and lifetime.

ChemInform Abstract: UV Absorption Spectra and Kinetics of the Self Reaction of CFCl2CH2O2 and CF2ClCH2O2 Radicals in the Gas Phase at 298 K.

The ultraviolet absorption spectra of the peroxy radicals derived from hydrochlorofluorocarbons 141b and 142b, (CFCl2CH2O2 and CF2ClCH2O2, respectively), and the kinetics of their self reactions have been studied in the gas phase at 298 K using a pulse radiolysis technique. Absorption cross sections were quantified over the wavelength range 220–300 nm. Measured absorption cross sections at 250 nm were indistinguishable within the experimental uncertainties (≈10%) and yield; Errors represent the sum of statistical uncertainty and our estimate of potential systematic errors. Our absorption cross section data were then used to derive the observed self reaction rate constants for reactions (1) and (2), defined as −d[RO2]/dt = 2k[RO2]2 (R = CFCl2CH2 or CF2ClCH2), of k1obs = (4.36 ± 0.64) × 10−12 and k2obs = (4.13 ± 0.58) × 10−12 cm3 molecule−1 s−1, quoted errors represent 2σ. These results are discussed with respect to previous studies of the absorption spectra and kinetics of peroxy radicals.

PHOTOLYSIS AND LIFETIME OF NO2, N2O AND HNO3 USING ANALYTICAL SOFTWARE PROGRAM

In this research photolysis of NO 2, N 2 O and HNO 3 for vast range of altitudes was investigated using the absorption cross-section data provided by NASA. The calculations were made using a special software computer program. Also the lifetimes of NO 2, N 2 O and HNO 3 were calculated. The investigation revealed that the lifetime due to photolysis will be nearly steady and short for NO 2, and will be as long (as there is no overlap with solar fluxes below 50 km altitude) for N 2 O . As for nitric acid HNO 3 the lifetime started to increase from 1 day at 25 km altitude to 10 days at the surface of the earth.